1. Field of the Invention
The present invention relates to an ink jet head mounted on an ink jet recording apparatus applied to, for example, a printer or a facsimile machine.
2. Description of the Related Art
Conventionally, an ink jet recording apparatus for recording letters or images on a recording medium using a recording head for expelling ink from a plurality of nozzles is known. In such an ink jet recording apparatus, the recording head opposed to the recording medium is provided in a head holder, and the head holder is mounted on a carriage to scan the recording medium in a direction orthogonal to the direction of conveyance of the recording medium.
FIG. 6 is an exploded perspective view showing the main part of an example of such conventional recording head. FIG. 7A is a side sectional view and FIG. 7B is a frontal sectional view taken along line 7Bxe2x80x947B in FIG. 7A showing the main part of the conventional recording head. As shown in FIGS. 6 and 7, a plurality of channels 102 are provided side by side in an actuator plate 101 formed of piezoelectric ceramic in its width direction. The channels 102 are separated from one another by side walls 103. One end portion of the channels 102 in the longitudinal direction extends to one end face of the actuator plate 101, while the other end portion does not extend to the other end face, with the depth being gradually decreased. An electrode 105 for applying a drive voltage is formed on the surface of the opening side of both side walls 103 and 103 of each channel 102 over the longitudinal direction.
A cover plate 107 is joined by an adhesive 109 to the opening side of the channels 102 in the actuator plate 101. The gap between the shallow portions of the rear end portion of the channels 102 in the actuator plate 101 and the cover plate 107 is sealed with sealant 110. The cover plate 107 has a common ink chamber 111 which is a concave portion communicating with the shallow, other end portion of the channels 102, and an ink supply port 112 piercing from the bottom portion of the common ink chamber 111 in the opposite direction from the channels 102. An ink flow path 114 of a flow path block 113 communicates with and opens to the ink supply port 112. Further, a filter 116 is attached to an end portion of the ink flow path 114 of the flow path block 113 on the side of the ink supply port 112.
A nozzle plate 115 is affixed and joined by an adhesive to an end face where the channels 102 of the joined body of the actuator plate 101 and the cover plate 107 are open. The width of the nozzle plate 115 is larger than the width of the end face of the joined body and the length of the nozzle plate 115 is larger than the length of the end face of the joined body. Nozzle openings 117 are formed in the nozzle plate 115 at positions opposed to the channels 102, respectively. Further, as shown in FIGS. 7A, 7B, a nozzle plate cover 118 is fixed by the adhesive to the rear surface of the nozzle plate 115 so as to cover the outer peripheral surface of an end portion of the joined body of the actuator plate 101 and the cover plate 107 and to cover the rear surface of the nozzle plate 115.
It is to be noted that a wiring board 120 is fixedly attached to a surface of the actuator plate 101 which is opposite to the side of the nozzle plate 115 and opposite to the side of the cover plate 107. Wirings 122 connected to the electrodes 105, respectively, using bonding wires 121, a flexible substrate, or the like are formed on the wiring board 120, such that drive voltage can be applied to the electrodes 105 via the wirings 122.
In the recording head described above, the channels 102 are filled with ink from the ink flow path 113 via the ink supply port 112 and the common ink chamber 111. By applying a predetermined drive voltage on side walls 103 on both sides of a predetermined channel 102 via the electrodes 105, the side walls 103 are deformed to change the volume in the predetermined channel 102, which leads to expulsion of ink in the channel 102 from the nozzle opening 117.
For example, as shown in FIG. 8 which is a frontal sectional view showing the main part, in the case where ink is expelled from a nozzle opening 117 corresponding to a channel 102a, positive drive voltage is applied to electrodes 105a and 105b in the channel 102a while electrodes 105c and 105d opposed to the electrodes 105a and 105b, respectively, are grounded. By this, drive electric field toward the channel 102a acts on the side walls 103a and 103b. When this is orthogonal to the direction of polarization of the actuator plate 101 formed of piezoelectric ceramic, due to a piezoelectric thickness sliding effect, the side walls 103a and 103b are deformed to be warped toward the channel 102, the volume in the channel 102 is decreased to increase the pressure, and ink is expelled from the nozzle opening 117.
Further, in such a recording head, a water-repellent film having water repellency is provided on the surface of the nozzle plate 115 which is opposed to a printed material for the purpose of preventing a head from getting dirty due to attachment of ink, preventing clogging of the nozzle openings 117, and the like. Further, the head end face is cleaned at predetermined regular time intervals or at a desired time. The cleaning is typically carried out by wiping out the face of the nozzle plate 115 which is opposed to a printed material with a wiper formed of, for example, rubber which has a relatively high hardness (Hs 40-50) and does not swell.
However, in the structure of the recording head described in the above, the whole thickness of the nozzle plate 115 is exposed. Therefore, there is a problem that, when the nozzle plate 115 is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate 115 off the wiper or the printed material acts on the exposed nozzle plate 115, and thus, the nozzle plate 115 is peeled off the end face of the joined body of the actuator plate 101 and the cover plate 107.
The present invention is made in view of these circumstances, and an object of the present invention is to provide an ink jet head in which a nozzle plate does not peel off the end face of a joined body of an actuator plate and a cover plate and the durability of which is expected to be improved.
In order to solve the above problem, according to a first aspect of the present invention, an ink jet head comprises: an actuator plate formed of piezoelectric ceramic with a plurality of channels formed therein, the channels opening to one surface and to one end face; a cover plate with a common ink chamber and an ink supply port formed therein, the common ink chamber being joined to the one surface of the actuator plate to seal a part of openings of the channels and to communicate with the channels, and the ink supply port piercing from the bottom portion of the common ink chamber in a direction opposite to the channels; a flow path block provided with a broad ink flow path, the inlet side thereof communicating with a narrow opening in proximity to an ink inflow port and the outlet side thereof communicating with the ink supply port; and a nozzle plate sealing the one end face of the actuator plate and having nozzle openings corresponding to the channels, respectively, the ink jet head expelling ink filled in the channels from the nozzle openings by applying drive voltage to electrodes provided on side walls of the channels and thereby changing the volume in the channels, and is characterized by comprising a nozzle plate cover joined to an outer side surface of the joined body of the actuator plate and the cover plate for surrounding the nozzle plate to protect the nozzle plate, and is characterized in that a surface of the nozzle plate which is opposed to a printed material is flush with a surface of the nozzle plate cover which is opposed to a printed material or protrudes from the surface of the nozzle plate cover in a predetermined range of height.
By structuring the ink jet head in this way, the whole thickness of the nozzle plate is not exposed. Therefore, when the nozzle plate is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate off the wiper or the printed material does not greatly act on a greatly exposed edge, and thus, the peeling of the nozzle plate off the end face of the joined body of the actuator plate and the cover plate is prevented and the durability can be expected to be improved.
According to a second aspect of the present invention, an ink jet head of the above first aspect of the invention is characterized in that the nozzle plate is formed so as to protrude from the outer edge of a front end of the joined body of the actuator plate and the cover plate, and the nozzle plate cover is shaped so as to surround the outer periphery and the rear surface of the nozzle plate.
By structuring the ink jet head in this way, action and effects similar to those of the above first aspect of the invention can be attained.
According to a third aspect of the present invention, an ink jet head of the above first or second aspect of the invention is characterized in that the surface of the nozzle plate which is opposed to a printed material protrudes from the surface of the nozzle plate cover which is opposed to a printed material by 0 xcexcm or more and half of the thickness of the nozzle plate or less.
When the surface of the nozzle plate which is opposed to a sprinted material protrudes from the surface of the nozzle plate cover which is opposed to a printed material by less than 0 xcexcm (a negative value, that is, when the surface of the nozzle plate which is opposed to a printed material receding with respect to the surface of the nozzle plate cover which is opposed to a printed material, ink remains in, for example, corner portions of the outer edges of the nozzle plate, and the wiping of the nozzle plate with the wiper is not carried out satisfactorily.
When the surface of the nozzle plate which is opposed to a printed material protrudes from the surface of the nozzle plate cover which is opposed to a printed material by more than half of the thickness of the nozzle plate, the peripheral surface of the nozzle plate is exposed more greatly than the nozzle plate cover for protection. When the nozzle plate is wiped out with a wiper, or, when a printed material (printed paper) is not properly fed and is jammed to be crumpled, force in the direction of peeling the nozzle plate off the wiper or the printed material acts on the exposed edges and the side surface of the nozzle plate, and thus, the nozzle plate is liable to peel off the end face of the joined body of the actuator plate and the cover plate.